Switching from gas to electric hot water and heating
We just recently finished a renovation/extension in Seattle of a 1920s house (2 story + basement) that included installing 10kw of solar panels. The entire roof was replaced with R-50 insulation and all the new walls are R-22 (about 1/3 of the existing structure). Pre-renovation blower door test was 0.35 ACHn – we haven’t done an updated test yet.
For heating, we have a 1.5 ton Mitsubishi ducted heat pump for the upstairs floor (830 sqft). For the basement (500 sqft) and main floor (780 sqft) we have a gas water boiler with a hydronic air handler to a ducted air furnace. On the main floor we also have hydronic in-floor heat for 200 sqft of concrete floor – short term experience is this keeps at least half of the main floor reasonably warm.
With the panels, we’d like to switch our gas hot water and heating on the main/basement floor to electric. Here are the options I’m considering:
Option 1. Replace main floor and basement with another 1.5 ton Mitsubishi ducted heat pump. This would have the advantage of cooling but we find having cooling in the bedrooms only to be more than sufficient,. Replace gas water boiler with hybrid heat pump water heater for domestic hot water and in-floor radiant heat
Option 2. Replace gas water boiler with a larger hybrid heat pump water heater with existing connections to hydronic air handler and in-floor radiant. The issue with this option is that the location of the gas boiler is in a conditioned basement space which as I understand would not be logical. It is just a storage/mechanical room so we could convert it to an unconditioned space. It is already partly insulated against the rest of the basement (2 internal walls) but more would insulation work would need to be done (ductwork, basement ceiling).
– Which of these options would be most efficient?
– Option 2 would be cheaper but does converting the mechanical room to unconditioned space make sense?
– Are there other options I should consider?
Thanks in advance!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part